Quasi co-located antenna ports for channel estimation

ABSTRACT

Systems and methods are disclosed for estimating one or more channel properties of a downlink from a cellular communications network based on quasi co-located antenna ports with respect to the one or more channel properties. In one embodiment, a user equipment receives a downlink subframe including a downlink control channel from the cellular communications network. The user equipment estimates one or more large-scale channel properties for an antenna port of interest in the downlink control channel based on a subset of reference signals that correspond to antenna ports in the cellular communications network that are quasi co-located with the antenna port of interest with respect to the one or more large-scale channel properties. As a result of using the quasi co-located antenna ports, estimation of the one or more large-scale channel properties is substantially improved.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/683,110, filed Aug. 22, 2017 and now issued as U.S. Pat. No.10,178,661, which is a continuation of U.S. patent application Ser. No.14/954,161, filed Nov. 30, 2015 and now issued as U.S. Pat. No.9,750,008, which is a continuation of U.S. patent application Ser. No.13/917,717, filed Jun. 14, 2013 and now issued as U.S. Pat. No.9,203,576, which claims the benefit of U.S. Prov. App. No. 61/679,335,filed Aug. 3, 2012, the disclosures of which are hereby incorporatedherein by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates to quasi co-located antenna ports in acellular communications network that can be utilized for estimation oflarge-scale, or long-term, channel properties.

BACKGROUND

Third Generation Partnership Project (3GPP) Long Term Evolution (LTE)uses Orthogonal Frequency Division Multiplexing (OFDM) in the downlinkand Discrete Fourier Transform (DFT) spread OFDM in the uplink. Thebasic LTE physical resource thus can be seen as a time-frequency grid asillustrated in FIG. 1, where each Resource Element (RE) corresponds toone subcarrier during one OFDM symbol interval on a particular antennaport. An antenna port is defined such that a channel over which a symbolon the antenna port is conveyed can be inferred from a channel overwhich another symbol on the same antenna port is conveyed. There is oneresource grid per antenna port. Notably, as discussed in Erik Dahlman etal., 4G LTE/LTE-Advanced for Mobile Broadband, § 10.1.1.7 (2011), anantenna port does not necessarily correspond to a specific physicalantenna but is instead a more general concept introduced, for example,to allow for beam-forming using multiple physical antennas. At least forthe downlink, an antenna port corresponds to the transmission of areference signal. Any data transmitted from the antenna port can thenrely on that reference signal for channel estimation for coherentdemodulation. Thus, if the same reference signal is transmitted frommultiple physical antennas, these physical antennas correspond to asingle antenna port. Similarly, if two different reference signals aretransmitted from the same set of physical antennas, this corresponds totwo separate antenna ports.

In the time domain, LTE downlink transmissions are organized into radioframes of 10 milliseconds (ms), where each radio frame consists of tenequally-sized subframes of 1 ms as illustrated in FIG. 2. A subframe isdivided into two slots, each of 0.5 ms time duration. Resourceallocation in LTE is described in terms of Resource Blocks (RBs), orPhysical RBs (PRBs), where a resource block corresponds to one slot inthe time domain and 12 contiguous 15 kilohertz (kHz) subcarriers in thefrequency domain. Two consecutive resource blocks in the time domainrepresent a resource block pair and correspond to the time interval uponwhich scheduling operates.

Transmissions in LTE are dynamically scheduled in each subframe where abase station transmits downlink assignments/uplink grants to certainUser Elements, or User Equipments (UEs), via a Physical Downlink ControlChannel (PDCCH) and, starting in LTE Release 11 (Rel-11), an enhancedPDCCH (ePDCCH). PDCCHs are transmitted in the first OFDM symbol(s) ineach subframe and span (more or less) the whole system bandwidth. A UEthat has decoded a downlink assignment, carried by a PDCCH, knows whichresource elements in the subframe that contain data aimed for the UE.Similarly, upon receiving an uplink grant, the UE knows whichtime/frequency resources it should transmit upon. In the LTE downlink,data is carried by a Physical Downlink Shared Channel (PDSCH). In theuplink, the corresponding link is referred to as a Physical UplinkShared Channel (PUSCH).

Definition of the ePDCCH is ongoing in 3GPP. It is likely that suchcontrol signaling will have similar functionalities as PDCCH. However, afundamental difference for ePDCCH is that ePDCCH will require UEspecific reference signals (i.e., Demodulation Reference Signals (DMRS))instead of cell specific reference signals (i.e., Common ReferenceSignals (CRS) for its demodulation. One advantage is that UE specificspatial processing may be exploited for ePDCCH.

Demodulation of data sent via the PDSCH requires estimation oflarge-scale channel properties of the radio channel. This channelestimation is performed using transmitted reference symbols, wherereference symbols are symbols of a Reference Signal (RS) and are knownto the receiver. In LTE, CRS reference symbols are transmitted in alldownlink subframes. In addition to assisting downlink channelestimation, the CRS reference symbols are also used for mobilitymeasurements performed by the UEs. LTE also supports UE specific RSreference symbols aimed only for assisting channel estimation fordemodulation purposes. FIG. 3 illustrates one example of mapping ofphysical control/data channels and signals onto resource elements withina RB pair forming a downlink subframe. In this example, PDCCHs occupythe first out of three possible OFDM symbols. So, in this particularcase, the mapping of data could start at the second OFDM symbol. Sincethe CRS is common to all UEs in the cell, the transmission of the CRScannot be easily adapted to suit the needs of a particular UE. This isin contrast to UE specific RSs where each UE has a UE specific RS of itsown placed in the data region of FIG. 3 as part of the PDSCH.

The length of the control region, which can vary on a subframe basis, isconveyed in the Physical Control Format Indicator Channel (PCFICH). ThePCFICH is transmitted within the control region at locations known bythe UEs. After a UE has decoded the PCFICH, the UE knows the size of thecontrol region and in which OFDM symbol the data transmission begins. APhysical Hybrid-Automatic Repeat Request (HARD) indicator, which carriesACK/NACK responses to a UE to inform the UE of whether a correspondinguplink data transmission in a previous subframe was successfully decodedby the base station, is also transmitted in the control region.

In LTE Release 10 (Rel-10), all control messages to UEs are demodulatedusing the CRSs. Therefore, the control messages have cell wide coverageto reach all UEs in the cell. An exception is the PrimarySynchronization Signal (PSS) and the Secondary Synchronization Signal(SSS), which are stand-alone and do not need reception of a CRS beforedemodulation. The first one to four OFDM symbols in a subframe,depending on the configuration, are reserved for such controlinformation. Control messages can be categorized into control messagesthat need to be sent only to one UE in the cell (i.e., UE-specificcontrol messages) and control messages that need to be sent to all UEsin the cell or some subset of the UEs in the cell numbering more thanone (i.e., common control messages).

As illustrated in FIG. 4, control messages of the PDCCH type aredemodulated using CRSs and transmitted in multiples of units calledControl Channel Elements (CCEs), where each CCE contains 36 REs. A PDCCHmay have an Aggregation Level (AL) of 1, 2, 4, or 8 CCEs to allow forlink adaptation of the control message. Furthermore, each CCE is mappedto 9 Resource Element Groups (REGs) consisting of 4 REs each. These REGsare distributed over the whole system bandwidth to provide frequencydiversity for a CCE. Hence, a PDCCH, which consists of up to 8 CCEs,spans the entire system bandwidth in the first one to four OFDM symbols,depending on the configuration.

In LTE Rel-11, it has been agreed to introduce UE-specific transmissionof control information in the form of enhanced control channels. Morespecifically, it has been agreed to allow transmission of genericcontrol messages to a UE using transmissions based on UE-specific RSsplaced in the data region. This is commonly known as an ePDCCH, anenhanced Physical HARQ Indicator Channel (ePHICH), etc. FIG. 5illustrates a downlink subframe showing 10 RB pairs and configuration ofthree ePDCCH regions of size 1 RB pair each. The remaining RB pairs canbe used for PDSCH transmissions. For ePDCCH in LTE Rel-11, it has beenagreed to use antenna port p∈{107,108,109,110} for demodulation asillustrated in FIG. 6 for normal subframes and normal cyclic prefix.More specifically, FIG. 6 illustrates an example of RE locations forUE-specific reference symbols (i.e., DMRS reference symbols) used forePDCCH in LTE for one PRB pair. Note that, starting in LTE Rel. 11, morethan one UE can, in some cases, unknowingly of each other use the sameDMRS reference symbols to demodulate their respective ePDCCH messages.As such, “UE specific” should be interpreted as seen from the UEsperspective. RS ports R7 and R9 represent the DMRS reference symbolscorresponding to antenna port 107 and 109, respectively. In addition,antenna ports 108 and 110 can be obtained by applying an orthogonalcover (1, −1) over adjacent pairs of RS ports R7 and R9, respectively.The ePDCCH enables precoding gains to be achieved for the controlchannels. Another benefit of the ePDCCH is that different PRB pairs (orenhanced control regions) can be allocated to different cells ordifferent transmission points within a cell and, as such, inter-cell orinter-point interference coordination between control channels can beachieved. This is especially useful for heterogeneous network scenarios,as discussed below.

The concept of a point is heavily used in conjunction with techniquesfor Coordinated Multi-Point (CoMP). In this context, a point correspondsto a set of antennas covering essentially the same geographical area ina similar manner. Thus, a point might correspond to one of multiplesectors at a site (i.e., one of two or more sectors of a cell served byan enhanced Node B (eNB)), but it may also correspond to a site havingone or more antennas all intending to cover a similar geographical area.Often, different points represent different sites. Antennas correspondto different points when they are sufficiently geographically separatedand/or have antenna diagrams pointing in sufficiently differentdirections. Techniques for CoMP entail introducing dependencies in thescheduling or transmission/reception among different points, in contrastto conventional cellular systems where a point from a scheduling pointof view is operated more or less independently from the other points.Downlink CoMP operations may include, for example, serving a certain UEfrom multiple points, either at different time instances or for a givensubframe, on overlapping or non-overlapping parts of the spectrum.Dynamic switching between transmission points serving a certain UE isoften termed as Dynamic Point Selection (DPS). Simultaneously serving aUE from multiple points on overlapping resources is often termed asJoint Transmission (JT). Point selection may be based on, for example,instantaneous conditions of the channels, interference, or traffic. CoMPoperations are intended to be performed for data channels (e.g., PDSCH)and/or control channels (e.g., ePDCCH).

The same ePDCCH region can be used by different transmission pointswithin a cell or belong to different cells that are not highlyinterfering with respect to one another. A typical case is the sharedcell scenario illustrated in FIG. 7. As illustrated, a heterogeneousnetwork includes a macro node, or macro base station, and multiple lowerpower pico nodes, or pico base stations, within a coverage area of themacro node. The same ePDCCH region can be used by the macro node and thepico nodes. Note that, throughout this application, nodes or points in anetwork are often referred to as being of a certain type, e.g., “macro”or “pico.” Unless explicitly stated otherwise, this should not beinterpreted as an absolute quantification of the role of the node/pointin the network but rather as a convenient way of discussing the roles ofdifferent nodes/points relative each other. Thus, a discussion aboutmacro and pico nodes/points could for example just as well be applicableto the interaction between micro and femto nodes/points.

For pico nodes that are geographically separated, such as pico nodes Band C, the same ePDCCH region can be re-used. In this manner the totalcontrol channel capacity in the shared cell will increase since a givenPRB resource is re-used, potentially multiple times, in different partsof the cell. This ensures that area splitting gains are obtained. Anexample is given in FIG. 8 where pico nodes B and C share the sameePDCCH regions. Conversely, due to proximity, pico nodes A and B andpico nodes A and C are at risk of interfering with each other and,therefore, pico node A is assigned an ePDCCH region that isnon-overlapping with the shared ePDCCH regions of the pico nodes B andC. Interference coordination between pico nodes A and B, or equivalentlytransmission points A and B, within the shared macro cell is therebyachieved. Likewise, interference coordination between pico nodes A andC, or equivalently transmission points A and C, within the shared macrocell is thereby achieved. In some cases, a UE may need to receive partof the ePDCCH signaling from the macro cell and the other part of theePDCCH signaling from the nearby pico cell. This area splitting andcontrol channel frequency coordination is not possible with the PDCCHsince the PDCCH spans the whole bandwidth. Also, the PDCCH does notprovide possibility to use UE specific precoding since it relies on theuse of CRS for demodulation.

FIG. 9 illustrates an ePDCCH that, similar to the CCE in the PDCCH, isdivided into multiple groups and mapped to one of the enhanced controlregions of a subframe. Note that in FIG. 9, the ePDCCH regions do notstart at OFDM symbol zero in order to accommodate simultaneoustransmission of a PDCCH in the subframe. However, there may be carriertypes in future LTE releases that do not have a PDCCH, in which case theePDCCH regions could start from OFDM symbol zero within the subframe.

Even if ePDCCH enables UE specific precoding and localized transmissionas discussed above, it can, in some cases, be useful to be able totransmit ePDCCH in a broadcasted, wide area coverage fashion. This isuseful if the base station (i.e., eNB) does not have reliableinformation to perform precoding towards a certain UE. In thissituation, a wide area coverage transmission is more robust. Anothercase is when the particular control message is intended for more thanone UE. In this case, UE specific precoding cannot be used. An exampleis the transmission of the common control information using PDCCH (i.e.,in the Common Search Space (CSS)). In any of these cases, a distributedtransmission over multiple ePDCCH regions within a subframe can be used.One example of such distribution is illustrated in FIG. 10 where thefour parts belonging to the same ePDCCH are distributed over multipleenhanced control regions within a subframe. It has been agreed in the3GPP ePDCCH development that both distributed and localized transmissionof an ePDCCH should be supported. When distributed transmission ofePDCCH is used, it is also beneficial if antenna diversity can beachieved to maximize the diversity order of an ePDCCH message. On theother hand, sometimes only wideband channel quality and widebandprecoding information is available at the base station, in which case itcould be useful to perform a distributed transmission but with UEspecific, wideband precoding.

As discussed above, enhanced control signaling, such as ePDCCH in LTE,offers many advantages. However, advanced network architectures (e.g.,heterogeneous network architectures) and downlink CoMP lead to issuesthat must be solved. In particular, as discussed below, the inventorshave found that there is a need for systems and methods for improvedchannel estimation techniques.

SUMMARY

Systems and methods are disclosed for estimating one or more channelproperties of a downlink from a cellular communications network based onquasi co-located antenna ports with respect to the one or more channelproperties. In one embodiment, a wireless device receives a downlinksubframe including a downlink control channel from the cellularcommunications network. The wireless device estimates one or morelarge-scale channel properties for an antenna port of interest in thedownlink control channel based on a subset of RSs that correspond toantenna ports in the cellular communications network that are quasico-located with the antenna port of interest with respect to the one ormore channel properties. By estimating the one or more channelproperties based on the subset of the RSs that correspond to the quasico-located antenna ports rather than a single RS that corresponds to theantenna port of interest for which the one or more large-scale channelproperties are estimated, estimation of the one or more large-scalechannel properties is substantially improved.

In one embodiment, the cellular communications network is a Long TermEvolution (LTE) cellular communications network, and the downlinkcontrol channel is an enhanced Public Downlink Control Channel (ePDCCH).In one embodiment, the wireless device does not assume that antennaports that correspond to RSs in the ePDCCH are quasi co-located withrespect to large-scale channel properties between antenna ports andbetween physical resource blocks within the downlink subframe. In oneparticular embodiment, the wireless device determines whether a DownlinkControl Information (DCI) message in the ePDCCH is associated with twoor more Demodulation RS (DMRS) ports and/or two or more physicalresource blocks. If so, the antenna ports that are quasi co-located withrespect to the one or more channel properties of the RS port within theePDCCH include antenna ports, and preferably all antenna ports,associated with the DCI message.

In another particular embodiment, ePDCCH resources forming a searchspace of the wireless device are divided into two or more sets of ePDCCHresources where antenna ports within the same set of ePDCCH resourcesmust be quasi co-located at least with respect to the one or morelarge-scale channel properties according to one or more predefined rulesfor the cellular communications network. In this embodiment, thewireless device estimates the one or more large-scale channel propertiesfor the RS port within the ePDCCH based on a subset of the RSs thatcorrespond to antenna ports that are within the same set of ePDCCHresources and, therefore, are quasi co-located with respect to the oneor more large-scale channel properties.

In another particular embodiment, ePDCCH resources forming a searchspace of the wireless device are divided into two or more sets of ePDCCHresources. The wireless device receives signaling from the cellularcommunications network that indicates whether antenna ports within thesame set of ePDCCH resources within the downlink subframe are quasico-located with respect to the one or more large-scale channelproperties. If so, the wireless device estimates the one or morelarge-scale channel properties for the RS port within the ePDCCH basedon a subset of the RSs that correspond to antenna ports that are withinthe same set of ePDCCH resources and, therefore, are quasi co-locatedwith respect to the one or more large-scale channel properties. In onefurther embodiment, the wireless device may receive signaling from thecellular communications network that indicates whether antenna portswithin two or more different sets of ePDCCH resources within thedownlink subframe are quasi co-located with respect to the one or morelarge-scale channel properties. If the antenna ports within two or moredifferent sets of ePDCCH resources are quasi co-located, then thewireless device estimates the one or more large-scale channel propertiesfor the RS port within the ePDCCH based on the subset of the RSs thatcorrespond to antenna ports that are within the two or more differentsets of ePDCCH resources and, therefore, are quasi co-located withrespect to the one or more large-scale channel properties.

In one embodiment, a base station in a cellular communications networkincludes a radio subsystem and a processing subsystem associated withthe radio subsystem. The processing subsystem provides, via the radiosubsystem, a downlink subframe that includes multiple RSs correspondingto multiple antenna ports according to one or more predefined rules thatdefine one or more subsets of the antenna ports that must be quasico-located within a downlink control channel of a downlink subframe. Inthis manner, the base station enables a wireless device to, for example,estimate one or more large-scale channel properties based on a subset ofthe RSs within the downlink subframe corresponding to antenna ports thatare quasi co-located with respect to the one or more large-scale channelproperties.

In another embodiment, a base station in a cellular communicationsnetwork includes a radio subsystem and a processing subsystem associatedwith the radio subsystem. The processing subsystem sends, via the radiosubsystem, information to a wireless device that is indicative ofantenna ports that are quasi co-located within a downlink controlchannel of a subframe of a downlink from the cellular communicationsnetwork. Using this information, the wireless device is enabled to, forexample, estimate one or more large-scale channel properties based onRSs that correspond to antenna ports that are quasi co-located withrespect to the one or more large-scale channel properties.

Those skilled in the art will appreciate the scope of the presentdisclosure and realize additional aspects thereof after reading thefollowing detailed description of the preferred embodiments inassociation with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the disclosure, andtogether with the description serve to explain the principles of thedisclosure.

FIG. 1 illustrates a resource block of a downlink in a 3^(rd) GenerationPartnership Project (3GPP) Long Term Evolution (LTE) cellularcommunications network;

FIG. 2 illustrates the time-domain structure of a downlink in a 3GPP LTEcellular communications network;

FIG. 3 illustrates mapping of LTE physical control signaling, data link,and Common Reference Signals (CRS) within a downlink subframe in a 3GPPLTE cellular communications network;

FIG. 4 illustrates mapping of one Control Channel Element (CCE)belonging to a Public Downlink Control Channel (PDCCH) to the controlregion within a downlink subframe in a 3GPP LTE cellular communicationsnetwork;

FIG. 5 illustrates enhanced control regions, or enhanced PDCCH (ePDCCH)regions, in a downlink subframe in a 3GPP LTE cellular communicationsnetwork;

FIG. 6 illustrates an example of Demodulation Reference Signal (DMRS)ports used for ePDCCH, where the DMRS ports correspond to antenna ports;

FIG. 7 illustrates a heterogeneous network architecture for a cellularcommunications network;

FIG. 8 illustrates different ePDCCH resource regions where some ePDCCHresource regions are reused by pico nodes in the heterogeneous networkarchitecture without interference;

FIG. 9 illustrates a downlink subframe including a CCE belonging to anePDCCH mapped to one of the ePDCCH regions in the downlink subframe;

FIG. 10 illustrates a downlink subframe including a CCE belonging to anePDCCH mapped to multiple ePDCCH regions to achieve distributedtransmission and frequency diversity or subband precoding;

FIG. 11 illustrates a cellular communications network in which awireless device performs channel estimation for a downlink controlchannel using reference signals that correspond to quasi co-locatedantenna ports according to one embodiment of the present disclosure;

FIG. 12A illustrates one example of a cellular communications network inwhich reference signals corresponding to quasi co-located antenna portswithin a downlink subframe are utilized for channel estimation of adownlink control channel according to one embodiment of the presentdisclosure;

FIG. 12B illustrates another example of a cellular communicationsnetwork in which reference signals corresponding to quasi co-locatedantenna ports within a downlink subframe are utilized for channelestimation for a downlink control channel according to one embodiment ofthe present disclosure;

FIG. 13 illustrates the operation of the cellular communications networkof FIG. 11 to provide channel estimation for a downlink control channelusing reference signals in a downlink subframe corresponding to quasico-located antenna ports according to one embodiment of the presentdisclosure;

FIG. 14 illustrates the operation of the cellular communications networkof FIG. 11 to provide channel estimation for a downlink control channelusing reference signals corresponding to quasi co-located antenna portsin which the quasi co-located antenna ports are signaled by the cellularcommunications network according to one embodiment of the presentdisclosure;

FIG. 15 illustrates the operation of the cellular communications networkof FIG. 11 to provide channel estimation for a downlink control channelusing reference signals corresponding to quasi co-located antenna portsin which the quasi co-located antenna ports are predefined for thecellular communications network according to one embodiment of thepresent disclosure;

FIG. 16 illustrates multiple ePDCCH resource regions within a subframe;

FIGS. 17A, 17B, and 17C illustrate different CRS ports that correspondto different antenna ports that are found in the ePDCCH resource regionsof FIG. 16;

FIGS. 18A and 18B illustrate different Demodulation Reference Signal(DMRS) ports that correspond to different antenna ports that are foundin the ePDCCH resource regions of FIG. 16;

FIG. 19 illustrates different Channel State Information Reference Signal(CSI-RS) ports that correspond to different antenna ports that are foundin the ePDCCH resource regions of FIG. 16;

FIG. 20 illustrates the operation of the wireless device of FIG. 11 toperform channel estimation for a Reference Signal (RS) port within anePDCCH region based on RSs that correspond to quasi co-located antennaports according to one embodiment of the present disclosure;

FIG. 21 illustrates the operation of the wireless device of FIG. 11 toperform channel estimation for an RS port within an ePDCCH region basedon RSs that correspond to quasi co-located antenna ports according toanother embodiment of the present disclosure in which antenna portswithin the same set of ePDCCH resources are predefined as being quasico-located;

FIG. 22 illustrates the operation of the base station of the cellularcommunications network of FIG. 11 to transmit ePDCCH according to one ormore predefined rules indicating that all antenna ports in a set ofePDCCH resources must be quasi co-located according to one embodiment ofthe present disclosure;

FIG. 23 illustrates the operation of the wireless device of FIG. 11 toperform channel estimation for an RS port within an ePDCCH region basedon RSs that correspond to quasi co-located antenna ports according toanother embodiment of the present disclosure in which antenna portswithin the same set of ePDCCH resources and potentially different setsof ePDCCH resources that are quasi co-located are signaled to thewireless device;

FIG. 24 illustrates one example of the process of FIG. 23 according toone embodiment of the present disclosure;

FIG. 25 is a block diagram of a wireless device according to oneembodiment of the present disclosure; and

FIG. 26 is a block diagram of a base station according to one embodimentof the present disclosure.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the embodiments andillustrate the best mode of practicing the embodiments. Upon reading thefollowing description in light of the accompanying drawing figures,those skilled in the art will understand the concepts of the disclosureand will recognize applications of these concepts not particularlyaddressed herein. It should be understood that these concepts andapplications fall within the scope of the disclosure and theaccompanying claims.

Note that although terminology from the 3^(rd) Generation PartnershipProject (3GPP) Long Term Evolution (LTE) specifications is used in muchof the description below to exemplify preferred embodiments of thepresent disclosure, this should not be seen as limiting the scope of thepresent disclosure to only 3GPP LTE. Other wireless systems such as, butnot limited to, Wideband Code Division Multiple Access (WCDMA),Worldwide Interoperability for Microwave Access (WiMax), Ultra MobileBroadband (UMB), and Global System for Mobile communications (GSM) mayalso benefit from exploiting the concepts disclosed herein.

Before discussing various embodiments of the present disclosure, adiscussion a fundamental problem discovered by the inventors isbeneficial. One of the principles guiding the design of the 3GPP LTEcellular communications network is transparency of the network to theUser Equipment (UE). In other words, in LTE, the UE is able todemodulate and decode its intended channels without specific knowledgeof scheduling assignments for other UEs or network deployments. However,in advanced scenarios such as downlink Coordinated Multi-Point (CoMP)and distributed uplink and downlink, this concept of networktransparency results in the fact that the UE cannot assume thatreference signals within a subframe originate from the same transmitpoints in the cellular communications network.

For example, in LTE, different Downlink Control Information (DCI)messages on an enhanced Physical Downlink Control Channel (ePDCCH) maybe transmitted from ports belonging to different transmission points.Even though there are several reasons for serving a UE with controlsignaling from different points, one application consists ofdistributing parts of the scheduling algorithm at different points suchthat, for example, downlink (DL) transmissions are associated to adifferent point than uplink (UL) transmissions. This scenario isreferred to herein as a distributed uplink and downlink scenario. Insuch a case, it makes sense to schedule downlink and uplinktransmissions with control signaling provided directly from therespective points. As another example, a UE may be served with paralleldata transmissions from different points (e.g., for increasing data rateor during handover between points). As another example, system controlinformation can be transmitted from a “master” point and datatransmissions can be transmitted from other points, typically associatedwith pico nodes. In all the above examples, it makes sense to have thepossibility to serve the UE with control signaling on ePDCCH fromdifferent points in the same subframe. However, due to networktransparency, UEs are not aware of the geographical location from whicheach Reference Signal (RS) port is transmitted.

Demodulation RSs (DMRSs), or UE specific RSs, are employed fordemodulation of data channels and possibly certain control channels(i.e., ePDCCH). A DMRS relieves the UE from having to know many of theproperties of the transmission and thus allows flexible transmissionschemes to be used from the network side. This is referred to astransmission transparency (with respect to the UE). However, theinventors have found that the estimation accuracy of a DMRS may not besufficient in some situations.

Geographical separation of RS ports implies that instantaneous channelcoefficients from each port towards the UE are in general different.Furthermore, even statistical properties of the channels for differentRS ports and RS types may be significantly different. Examples of suchstatistical properties include received power for each port, delayspread, Doppler spread, received timing (i.e., timing of a firstsignificant channel tap), a number of significant channel taps,frequency shift, average gain, and average delay. In LTE, nothing can beassumed about the properties of the channel corresponding to an antennaport based on the properties of the channel of another antenna port.This is in fact a key part of maintaining transmission transparency.

Based on the above observations, the inventors have found that the UEneeds to perform independent estimation for each RS port of interest foreach RS. In general, this results in occasionally inadequate channelestimation quality for certain RS ports, leading to undesirable link andsystem performance degradation. However, the inventors have also foundthat, even though in general the channel from each antenna port to eachUE receive port is substantially unique, some statistical properties andpropagation parameters may be common or similar among different antennaports, depending on whether or not the different antenna ports originatefrom the same transmit point. Such properties include, for example, areceived power level for each antenna port, a delay spread, a Dopplerspread, received timing (i.e., timing of a first significant channeltap), frequency shift, average gain, and average delay. Thus, thechannel estimation for one RS port may be performed based on other RSports having sufficiently similar channel properties.

Typically, channel estimation algorithms perform a three step operation.A first step is estimating some statistical properties of the channel. Asecond step is generating an estimation filter based on the estimatedstatistical properties. A third step is applying the estimation filterto the received signal in order to obtain channel estimates. Theestimation filter may be equivalently applied in the time or thefrequency domain. Some channel estimator implementations may not bebased on the three step method described above, but still exploit thesame principles.

Obviously, accurate estimation of the filter parameters in the firststep leads to improved channel estimation. Even though it is often inprinciple possible for the UE to obtain such filter parameters fromobservation of the channel over a single subframe and for one RS port,it is usually possible for the UE to improve estimation accuracy of thefilter parameters by combining measurements associated with differentantenna ports (i.e., different RS transmissions) sharing similarstatistical properties. Furthermore, the channel estimation accuracy maybe improved by combining RSs associated with multiple PRBs.

Systems and methods are disclosed herein for estimating one or morechannel properties of a downlink from a cellular communications networkbased on quasi co-located antenna ports with respect to the one or morechannel properties. In the preferred embodiments described below,systems and methods are disclosed for estimating one or more channelproperties for an ePDCCH contained in a downlink subframe from a 3GPPLTE cellular communications network. Again, while the preferredembodiments disclosed herein focus on LTE, the concepts disclosed hereincan be utilized for estimating one or more channel properties for adownlink, and in particular a downlink control channel in a downlinksubframe, from other types of cellular communications networks.

In one embodiment, a wireless device estimates one or more large-scalechannel properties for an antenna port of interest within an ePDCCH of adownlink subframe received from a cellular communications network basedon a subset of RSs within the downlink subframe of the downlink. Thesubset of the RSs used for estimating the one or more large-scalechannel properties correspond to antenna ports in the cellularcommunications network that are quasi co-located with the antenna portof interest with respect to the one or more channel properties of theePDCCH. Preferably, in addition to the subset of the RSs that correspondto the quasi co-located antenna ports, estimation is also based on a RSthat corresponds to the antenna port of interest within the ePDCCH. Byestimating the one or more channel properties based on the subset of theRSs that correspond to the quasi co-located antenna ports rather thanonly the single RS that corresponds to the antenna port for which theone or more large-scale channel properties are estimated, estimation ofthe one or more large-scale channel properties is substantiallyimproved.

In this regard, FIG. 11 illustrates a cellular communications network 10that enables channel estimation based on RSs from quasi co-locatedantenna ports within a subframe according to one embodiment of thepresent disclosure. In this embodiment, the cellular communicationsnetwork 10 is a 3GPP LTE cellular communications network. Asillustrated, the cellular communications network 10 includes a RadioAccess Network (RAN) 12, which itself includes base stations (BSs) 14.The base stations 14 provide service to wireless devices, such aswireless device (WD) 16, located within corresponding service areas, orcells. The base stations 14 included in the RAN 12 can be macro or highpower base stations (i.e., enhanced Node Bs (eNBs)), pico or other lowpower base stations, or a combination thereof.

As illustrated in FIG. 11 and more specifically illustrated in FIG. 12A,in one particular embodiment, the RAN 12 and the WD 16 operate toprovide a distributed UL and DL for the WD 16. In particular, uplinkdata transmissions from the WD 16 (i.e., Physical Uplink Shared Channel(PUSCH)) are directed to and scheduled by a first point (e.g., a firstbase station 14) in the RAN 12 whereas DL data transmissions to the WD16 (i.e., Physical Downlink Shared Channel (PDSCH)) are transmitted fromand scheduled by a second point (e.g., a second base station 14) in theRAN 12. This may be beneficial, for example, in a heterogeneous networkscenario where the uplink data transmissions of the WD 16 are directedto and scheduled by a pico or low power base station 14 and the downlinkdata transmissions of the WD 16 are transmitted and scheduled by a macroor high power base station 14. In this case, an ePDCCH within a subframeof the downlink to the WD 16 may include both ePDCCH transmission(s)from the pico or low power base station 14 (e.g., an ePDCCH transmissionfor uplink scheduling) as well as ePDCCH transmission(s) from the macrobase station 14 (e.g., an ePDCCH transmission for downlink scheduling).

As discussed below, in order to demodulate the ePDCCH within thesubframe, the WD 16 needs to estimate one or more large-scale, orlong-term, channel properties for each RS port of interest within thesubframe. However, using conventional channel estimation techniques,channel estimation would need to be performed independently for each RSport of interest for each RS. This is because different RS ports for RSsof the same or different RS types within the same subframe can betransmitted from different points in the RAN 12 and, therefore, can havesignificantly different large-scale channel properties. Further, thesame RS port in different Physical Resource Blocks (PRBs) within thesame subframe can be transmitted from different points, which againmeans that the channel properties for those antenna ports can havesignificantly different large-scale channel properties. As noted above,using conventional channel estimation techniques to independentlyperform channel estimation for each RS port of interest for each RSwould lead to inadequate channel estimation quality for certain RSports, which would lead to undesirable link and system performancedegradation.

In order to improve channel estimation for ePDCCH, the WD 16 performsjoint estimation of one or more large-scale channel properties for eachRS port of interest within the ePDCCH of a downlink subframe based onRSs within the downlink subframe that correspond to antenna ports thatare quasi co-located. As used herein, two antenna ports are “quasico-located” if the large-scale channel properties of the channel overwhich a symbol on one antenna port is conveyed can be inferred from thechannel over which a symbol on the other antenna port is conveyed. Thelarge-scale channel properties preferably include one or more of delayspread, Doppler spread, Doppler shift, average gain, and average delay.In addition or alternatively, the large-scale channel properties caninclude one or more of received power for each port, received timing(i.e., timing of a first significant channel tap), a number ofsignificant channel taps, and frequency shift. By performing channelestimation based on the RSs corresponding to the quasi co-locatedantenna ports, a quality of the channel estimation is substantiallyimproved.

As illustrated in FIG. 11 and more specifically illustrated in FIG. 12B,in another particular embodiment, the RAN 12 provides downlink CoMP inwhich the downlink to the WD 16 is provided from multiple base stations14 in a coordinated manner. In this case, the ePDCCH within a subframeof the downlink to the WD 16 may include ePDCCH transmissions from twoor more transmit points (e.g., two or more base stations 14). Again, asdiscussed below, in order to demodulate the ePDCCH transmissions withinthe subframe, the WD 16 needs to estimate one or more large-scale, orlong-term, channel properties for each RS port of interest within thesubframe. However, using conventional channel estimation techniques,channel estimation would need to be performed independently for each RSport of interest for each RS. This would lead to inadequate channelestimation quality for certain RS ports, which would lead to undesirablelink and system performance degradation. In order to improve channelestimation for the ePDCCH, the WD 16 performs joint estimation of thelarge-scale channel properties of each RS port of interest based on RSswithin the subframe that correspond to antenna ports that are quasico-located.

FIG. 13 illustrates the operation of the cellular communications network10 of FIG. 11 according to one embodiment of the present disclosure. Asillustrated, the WD 16 receives a downlink subframe from the RAN 12,wherein the downlink subframe includes an ePDCCH and multiple RSs withinthe ePDCCH (step 100). The subframe may contain RS of different types,such as common reference signals (CRS) or channel state informationreference signals (CSI-RS). The ePDCCH utilizes PRBs located within oneor more ePDCCH resource regions within the subframe. Note that the RSsin the ePDCCH resource regions are more specifically referred to hereinas ePDCCH RSs on corresponding ePDCCH RS ports. The RSs in the downlinksubframe, and more specifically the ePDCCH RSs in the ePDCCH, caninclude:

-   -   multiple RSs of the same RS type in the same and/or different        PRB(s) (e.g., two or more DMRSs on two or more corresponding        DMRS ports in the same and/or different PRB(s)); and/or    -   multiple RSs of different RS types on the same and/or different        PRB(s) (e.g., a DMRS on a DMRS port and a Channel State        Information RS (CSI-RS) on a CSI-RS port in the same and/or        different PRB(s)).        Note that CSI-RS and CRS are wideband reference signals. In        other words, CSI-RS and CRS found across the entire bandwidth of        the downlink and not only in the EPDCCH. As such, when        performing channel analysis on, e.g., CSI-RS, the whole        bandwidth of CSI-RS can be used, not only the part that resides        within the EPDCCH RBs. Due to network transparency, the WD 16        does not assume that any particular RS on any particular RS port        is transmitted from the same transmit point across resource        blocks within the ePDCCH of the downlink subframe. For example,        a DMRS on DMRS port 7 cannot be assumed to be from the same        transmit point across different ePDCCH resource regions or even        across different PRBs in the same ePDCCH region.

The WD 16 then estimates one or more large-scale channel properties foran antenna port of interest of the downlink subframe based on a subsetof the RSs in the subframe and/or previous subframe(s) that correspondto antenna ports that are quasi co-located with the antenna port ofinterest with respect to the one or more large-scale channel properties(step 102). The antenna port of interest corresponds to an ePDCCH RSport of interest within a PRB in an ePDCCH resource region. In oneembodiment, the one or more large-scale channel properties are one ormore large-scale channel properties of a channel between a transmitpoint from which the antenna port of interest within the PRB originatedand the WD 16. The one or more large-scale channel properties preferablyinclude one or more of delay spread, Doppler spread, Doppler shift,average gain, and average delay. In addition or alternatively, the oneor more large-scale channel properties can include one or more ofreceived power for each port, received timing (i.e., timing of a firstsignificant channel tap), a number of significant channel taps, andfrequency shift.

Estimation of the one or more large-scale channel properties may beperformed using any suitable joint estimation technique that utilizesthe quasi co-located antenna ports to estimate the large-scale channelproperties for the desired antenna port. The estimation is preferablybased on the RS that corresponds to the antenna port of interest withinthe downlink subframe as well as the RSs that correspond to the antennaports that are quasi co-located with the antenna port of interest withrespect to the large-scale channel properties. The RSs that correspondto the antenna ports that are quasi co-located with the antenna port ofinterest with respect to the large-scale channel properties can includeRSs within the same downlink subframe as the antenna port of interestand/or RSs within one or more previous downlink subframes. Using RSs inone or previous subframes may be beneficial where, for example, CSI-RSare not transmitted in the downlink subframe of the antenna port ofinterest. Notably, the estimates generated in step 102 may be initialestimates for the one or more large-scale channel properties or updatedestimates of the one or more large-scale channel properties. Forinstance, estimation/updating across multiple subframes can be used toimprove the estimates of the one or more large-scale channel properties.

Lastly, the WD 16 utilizes the one or more large-scale channelproperties, or more specifically utilizes the estimates of the one ormore large-scale channel properties (step 104). More specifically, inone embodiment, the WD 16 utilizes the estimates of the one or morelarge-scale channel properties to configure one or more parameters of anestimation filter that is applied by the WD 16 in the time or thefrequency domain to perform the channel estimate used to receive thedownlink signal to enable reception and demodulation of the ePDCCH.

In 3GPP LTE, a key feature of the cellular communications network 10 isnetwork transparency. As a result of network transparency, the WD 16 isnot aware of the points in the RAN 12 from which the different antennaports originate. As such, in order for the WD 16 to estimate the one ormore large-scale channel properties in step 102 of FIG. 13, the WD 16must have knowledge of which antenna ports are quasi co-located with theantenna port of interest with respect to the one or more large-scalechannel properties. FIGS. 14 and 15 illustrate two embodiments in whichthe WD 16 obtains knowledge of the antenna ports that are quasico-located via signaling from the RAN 12 and via predefined rule(s) forthe cellular communications network 10.

More specifically, referring to FIG. 14, the WD 16 receives informationfrom the RAN 12 that is indicative of antenna ports that are quasico-located (step 200). In the preferred embodiment, the information fromthe RAN 12 is indicative of antenna ports that are quasi co-located withrespect to ePDCCH. This information may be explicitly signaled to the WD16 from the RAN 12 via Radio Resource Control (RRC) signaling or thelike. Alternatively, this information may be implicitly signaled to theWD 16 from the RAN 12 via, for example, DCI messages transmitted in theePDCCH. The information from the RAN 12 indicates which antenna portsare quasi co-located with respect to one or more large-scale channelproperties and physical resources over which those antenna ports arequasi co-located with respect to the one or more large-scale channelproperties. In one particular embodiment, the information from the RAN12 indicates which antenna ports are quasi co-located with respect toone or more large-scale channel properties within a subframe of adownlink to the WD 16 and physical resources with the subframe overwhich those antenna ports are quasi co-located with respect to the oneor more large-scale channel properties.

From this point, the process continues as described above with respectto steps 100-104 of FIG. 13. More specifically, the WD 16 receives adownlink subframe from the RAN 12, wherein the downlink subframeincludes an ePDCCH and multiple RSs within the ePDCCH (step 202). The WD16 then estimates one or more large-scale channel properties for anantenna port of interest within a subframe based on a subset of the RSsin the subframe and/or a previous subframe(s) that correspond to antennaports that are quasi co-located with the antenna port of interest withrespect to the one or more large-scale channel properties (step 204).The antenna port of interest corresponds to an ePDCCH RS port ofinterest within a PRB in an ePDCCH resource region. Here, the antennaports that are quasi co-located with respect to the one or morelarge-scale channel properties are indicated by the information receivedfrom the RAN 12 in step 200. In one embodiment, the one or morelarge-scale channel properties are one or more large-scale channelproperties of a channel between a transmit point from which the antennaport of interest originated and the WD 16. The one or more large-scalechannel properties preferably include one or more of delay spread,Doppler spread, Doppler shift, average gain, and average delay. Inaddition or alternatively, the one or more large-scale channelproperties can include one or more of received power for each port,received timing (i.e., timing of a first significant channel tap), anumber of significant channel taps, and frequency shift.

Estimation of the one or more large-scale channel properties may beperformed using any suitable joint estimation technique that utilizesthe quasi co-located antenna ports to estimate the large-scale channelproperties for the desired antenna port. The estimation is preferablybased on the RS that corresponds to the antenna port of interest of thedownlink subframe as well as the RSs that correspond to the antennaports that are quasi co-located with the antenna port of interest withrespect to the large-scale channel properties. The RSs that correspondto the antenna ports that are quasi co-located with the antenna port ofinterest with respect to the large-scale channel properties can includeRSs within the same downlink subframe as the antenna port of interestand/or RSs within one or more previous downlink subframes. Using RSs inone or previous subframes may be beneficial where, for example, CSI-RSare not transmitted in the downlink subframe of the antenna port ofinterest. Notably, the estimates generated in step 204 may be initialestimates for the one or more large-scale channel properties or updatedestimates of the one or more large-scale channel properties. Forinstance, estimation/updating across multiple subframes can be used toimprove the estimates of the one or more large-scale channel properties.

Lastly, the WD 16 utilizes the one or more large-scale channelproperties, and more specifically utilizes the estimates of the one ormore large-scale channel properties (step 206). More specifically, inone embodiment, the WD 16 utilizes the estimates of the one or morelarge-scale channel properties to configure one or more parameters of anestimation filter that is applied by the WD 16 in the time or thefrequency domain to perform channel estimation required for thereception and demodulation of the ePDCCH.

FIG. 15 illustrates the operation of the cellular communications network10 of FIG. 11 in which quasi co-located antenna ports are predefined forthe cellular communications network 10 according to one embodiment ofthe present disclosure. In one particular embodiment, the quasico-located antenna ports are defined by one or more specifications(i.e., 3GPP specifications) that define the operation of the cellularcommunications network 10. Thus, in this embodiment, the RAN 12transmits a downlink including RSs to the WD 16 according to one or morepredefined rules that define antenna ports that must be quasi co-located(step 300). More specifically, the downlink includes a downlink subframethat includes an ePDCCH. The RS ports of the RSs transmitted in theePDCCH correspond to antenna ports. The one or more predefined rulesdefine which of the antenna ports must be quasi co-located for theePDCCH. Thus, in other words, the one or more predefined rules definewhich of the RSs in the ePDCCH must originate from quasi co-locatedantenna ports. For example, as discussed below in detail, in oneembodiment, ePDCCH resources within a subframe are divided into two ormore sets of ePDCCH resources where the WD 16 is configured to search atleast two of the sets of ePDCCH resources. In this example, the one ormore predefined rules may state, for example, that antenna portscorresponding to all RS ports in the same set of ePDCCH resources mustbe quasi co-located. Note, however, that this example is not limiting.The rules may define antenna ports that must be quasi co-located in anydesired manner.

The WD 16 then estimates one or more large-scale channel properties foran antenna port of interest of the subframe based on a subset of the RSsin the subframe and/or a previous subframe(s) that correspond to antennaports that are quasi co-located with the antenna port of interest withrespect to the one or more large-scale channel properties (step 302).The antenna port of interest corresponds to an ePDCCH RS port ofinterest within a PRB in an ePDCCH resource region. Here, the antennaports that are quasi co-located with respect to the one or morelarge-scale channel properties are predefined for the cellularcommunications network 10. In one embodiment, the one or morelarge-scale channel properties are one or more large-scale channelproperties of a channel between a transmit point from which the antennaport of interest originated and the WD 16. The one or more large-scalechannel properties preferably include one or more of delay spread,Doppler spread, Doppler shift, average gain, and average delay. Inaddition or alternatively, the one or more large-scale channelproperties can include one or more of received power for each port,received timing (i.e., timing of a first significant channel tap), anumber of significant channel taps, and frequency shift.

Estimation of the one or more large-scale channel properties may beperformed using any suitable joint estimation technique that utilizesthe quasi co-located antenna ports to estimate the large-scale channelproperties for the desired antenna port. The estimation is preferablybased on the RS that corresponds to the antenna port of interest of thedownlink subframe as well as the RSs that correspond to the antennaports that are quasi co-located with the antenna port of interest withrespect to the large-scale channel properties. The RSs that correspondto the antenna ports that are quasi co-located with the antenna port ofinterest with respect to the large-scale channel properties can includeRSs within the same downlink subframe as the antenna port of interestand/or RSs within one or more previous downlink subframes. Using RSs inone or previous subframes may be beneficial where, for example, CSI-RSare not transmitted in the downlink subframe of the antenna port ofinterest. Notably, the estimates generated in step 302 may be initialestimates for the one or more large-scale channel properties or updatedestimates of the one or more large-scale channel properties. Forinstance, estimation/updating across multiple subframes can be used toimprove the estimates of the one or more large-scale channel properties.

Lastly, the WD 16 utilizes the one or more large-scale channelproperties, or more specifically utilizes the estimates of the one ormore large-scale channel properties (step 304). More specifically, inone embodiment, the WD 16 utilizes the one or more large-scale channelproperties to configure one or more parameters of an estimation filterthat is applied by the WD 16 in the time or the frequency domain to thereceived downlink signal to perform channel estimation required for thereception and demodulation of the ePDCCH.

In preferred embodiments of the present disclosure, channel estimationis performed for RS ports in ePDCCH resource regions within a subframeof a downlink from the RAN 12. Before discussing further details ofthese preferred embodiments, a discussion of ePDCCH resource regionswithin a subframe and various RSs and corresponding antenna ports thatcan be found in the ePDCCH resource regions is provided. In this regard,FIG. 16 illustrates a subframe of an LTE downlink that includes multipleePDCCH resource regions. In this example, each ePDCCH resource regionincludes a portion of a PRB in the first half of the subframe (i.e., thefirst slot of the subframe) and a PRB in the second half of the subframe(i.e., the second slot of the subframe). Note that, in anotherembodiment, there are no Orthogonal Frequency Division Multiplexing(OFDM) symbol intervals reserved for control information (e.g., PDCCH)at the start of the subframe, and each ePDCCH resource region includes afull PRB pair. Note that while four ePDCCH resource regions areillustrated in the example of FIG. 16, any number of ePDCCH resourceregions may be included in the subframe.

FIGS. 17A through 17C illustrate a Common Reference Signal (CRS) withina pair of PRBs in a subframe. A CRS is cell-specific RS that consists ofCRS reference symbols of predefined values inserted at time andfrequency locations within the PRBs in each subframe. FIG. 17Aillustrates a CRS port that corresponds to a single antenna port. Incontrast, FIGS. 17B and 17C illustrate CRS ports corresponding to twoand up to four antenna ports, respectively. As such, depending on theparticular configuration, each ePDCCH region within a subframe mayinclude from one up to four CRS ports (i.e., from one up to four antennaports carrying CRSs).

FIGS. 18A and 18B illustrate DMRS ports within a pair of PRBs in asubframe. A DMRS is a UE specific RS transmitted in PRBs assigned tothat specific UE. DMRSs are intended to be used for channel estimationfor PDSCH transmissions particularly for non-codebook-based precoding. ADMRS includes DMRS reference symbols of known values at known time andfrequency locations within the PRBs in the subframe. FIG. 18Aillustrates two DMRS ports using 12 DMRS resource elements (REs), wherethe two DMRS ports correspond to two antenna ports. Conversely, FIG. 18Billustrates eight DMRS ports using 24 DMRS REs, where the eight DMRSports correspond to eight antenna ports. Thus, depending on theparticular configuration, each ePDCCH region within a subframe mayinclude from one up to eight DMRS ports corresponding to from one up toeight antenna ports.

FIG. 19 illustrates CSI-RS ports within a pair of PRBs in a subframe. Asillustrated, there can be from one up to eight CSI-RSs within the pairof PRBs in the subframe on one up to eight CSI-RS ports, respectively.Each CSI-RS port is using two resource elements in the PRB pair.CSI-RS(s) can be utilized by a WD to acquire channel-state informationwhen DMRSs are used for channel estimation (e.g., in transmission mode 9of LTE Rel-10 and Rel-11). A CSI-RS includes CSI-RS reference symbols ofknown values at known time and frequency locations within the PRBs forthe corresponding CSI-RS port. As the CSI-RS(s) are transmitted in allPRBs of the system bandwidth, corresponding CSI-RS ports within theePDCCH resource regions of FIG. 16 can be found. Depending on theparticular configuration, each ePDCCH resource region within a subframemay include from one up to eight CSI-RS ports corresponding to from oneup to eight antenna ports.

FIG. 20 illustrates the operation of the WD 16 to estimate one or morelarge-scale channel properties for an RS port of interest (orcorrespondingly an antenna port of interest) within an ePDCCH resourceregion of a subframe using RSs that correspond to quasi co-locatedantenna ports according to one embodiment of the present disclosure. Inthis embodiment, the WD 16 does not assume that the antenna portscorresponding to DMRS ports are quasi co-located with respect to any ofthe large-scale channel properties between DMRS ports and between PRBswithin a subframe. In this embodiment, the WD 16 receives a downlinkfrom the RAN 12 (step 400) and determines that a DCI message of anePDCCH in a subframe of the downlink is associated with two or more DMRSports (e.g., for spatial diversity transmission) and/or two or more PRBs(step 402). In this case, the DCI message is an implicit signaling fromthe RAN 12 that all antenna ports associated with the DCI message arequasi co-located for the subframe. In other words, the WD 16 can inferfrom the DCI message that all antenna ports associated with the DCImessage are quasi co-located for the subframe. As such, the WD 16estimates one or more large-scale channel properties for the RS port ofinterest in the ePDCCH based on reference symbols in RS ports associatedwith the DCI message, where the RS ports associated with the DCI messagecorrespond to quasi co-located antenna ports (step 404). Lastly, the WD16 utilizes the one or more large-scale channel properties, as discussedabove (step 406).

Notably, the estimates of the large-scale channel properties can be usedfor channel estimation using DMRS. However, channel estimationalgorithms use Doppler shift, delay spread, and other large-scalechannel properties. These large-scale channel properties can be obtainedfrom, for example, CSI-RS(s) since CSI-RSs are wideband and periodic intime. However, in order to obtain the proper estimates of the channelproperties, the WD 16 must be ensured that the estimates of thelarge-scale channel properties obtained using CSI-RS(s) actually reflectthe same channel as the DMRS(s) of interest. This is done by, forexample, estimating the desired large-scale channel properties for theDMRS port of interest utilizing CSI-RS ports that are quasi co-locatedwith the DMRS port of interest.

When estimating the one or more large-scale channel properties based onCSI-RS(s) that are quasi co-located with a DMRS port of interest, the WD16 can determine which CSI-RS(s) are quasi co-located with the DMRS portof interest in any suitable manner. For instance, the WD 16 may beconfigured to receive two CSI-RS(s) (i.e., two CSI-RS ports). The WD 16can then determine which CSI-RS port(s) are quasi co-located with a DMRSport of interest based on resource allocation (i.e., which ePDCCHresources are received by the WD 16, which is indicated by the DCImessage). Thus, the CSI-RS(s) associated with the DCI message can beused to estimate the large-scale channel properties for the DMRS port ofinterest. In another embodiment, the WD 16 can determine which CSI-RSport(s) are quasi co-located with a DMRS port of interest based on thetype of transmission scheme. More specifically, the ePDCCH can betransmitted in localized mode or distributed mode. Then, DMRS ports forlocated ePDCCH reception can be defined as being quasi co-located with afirst CSI-RS port(s) and any DMRS ports for distributed ePDCCH receptioncan be defined as being quasi co-located with a second CSI-RS port(s).

FIG. 21 illustrates the operation of the WD 16 to estimate one or morelarge-scale channel properties for an RS port of interest (orcorrespondingly an antenna port of interest) within a set of ePDCCHresources within a subframe using RSs that correspond to quasico-located antenna ports according to one embodiment of the presentdisclosure. In this embodiment, the ePDCCH resource regions in thesubframe are divided into two or more sets of ePDCCH resources. Forexample, each ePDCCH resource region may correspond to a different setof ePDCCH resources. However, the sets of ePDCCH resources are notlimited thereto. For instance, a set of ePDCCH resources may includeePDCCH resources from multiple different ePDCCH resource regions withinthe subframe. Conversely, a set of ePDCCH resources may include only asubset of the resources in an ePDCCH resource region.

In this embodiment, the WD 16 does not assume that the antenna portscorresponding to DMRS ports are quasi co-located with respect to any ofthe large-scale channel properties between DMRS ports and between PRBsthat belong to different sets of ePDCCH resources. However, the WD 16does assume that DMRS ports, and potentially all or some other types ofRS ports, within the same set of ePDCCH resources are quasi co-locatedwith respect to one or more of the large-scale channel properties.

As illustrated, the WD 16 receives a downlink signal from the RAN 12(step 500). The WD 16 then estimates one or more large-scale channelproperties for an RS port in a set of ePDCCH resources within a subframeof the downlink signal based on the RSs that correspond to antenna portsin the set of ePDCCH resources (step 502). The RSs within the set ofePDCCH resources, or more specifically the reference symbols in the RSports within the set of ePDCCH resources, correspond to antenna portsthat are quasi co-located with respect to the one or more large-scalechannel properties according to the assumption noted above. Forinstance, the WD 16 may estimate the one or more large-scale channelproperties for a DMRS port of interest based on the CSI-RS port(s)within the same set of ePDCCH resources. Lastly, the WD 16 utilizes theone or more large-scale channel properties of the RS port as discussedabove (step 504).

FIG. 22 illustrates the operation of one of the base stations 14 in theRAN 12 to provide the downlink in accordance with the embodiment of FIG.21 according to one embodiment of the present disclosure. Asillustrated, the base station 14 configures sets of ePDCCH resources(step 600). More specifically, the base station 14 configures the WD 16to monitor one or more of the sets of ePDCCH resources (i.e., configuresa search space of the WD 16 for ePDCCH). The base station 14 thentransmits ePDCCH in accordance with the predefined rule(s) that allantenna ports in the same set of ePDCCH resources must be quasico-located (step 602). Notably, at the WD 16, antenna ports in differentsets of ePDCCH resources within a subframe are assumed to not be quasico-located.

FIG. 23 illustrates the operation of the cellular communications network10 according to another embodiment of the present disclosure. Thisembodiment is similar that that described above with respect to FIGS. 21and 22. However, in this embodiment, the RAN 12 provides information tothe WD 16 that indicates whether all RS ports or some defined subset ofRS ports within the same set of ePDCCH resources correspond to quasico-located antenna ports and, in some embodiments, information that isindicative of whether RS ports in two or more different sets of ePDCCHresources correspond to quasi co-located antenna ports. Morespecifically, as illustrated in FIG. 23, the RAN 12 configures a searchspace of the WD 16 for ePDCCH (step 700). In particular, the RAN 12configures the search space to include one or more sets of ePDCCHresources. The configuration of the search space may be performed, forexample, via RRC signaling.

In addition, the RAN 12 provides information to the WD 16, which isreferred to as quasi co-located antenna information, that is indicativeof which RS ports the WD 16 can assume correspond to quasi co-locatedantenna ports (step 702). In one preferred embodiment, the informationindicates whether the WD 16 can assume that all RS ports or some subsetof the RS ports within the same set of ePDCCH resources correspond toquasi co-located antenna ports. In some embodiments, the informationalso indicates whether the WD 16 can assume that all RS ports or somesubset of the RS ports within two or more different sets of ePDCCHresources correspond to quasi co-located antenna ports. So, for example,if there are two sets of ePDCCH resources, the information indicates:(1) whether the RS ports or some subset of the RS ports within the sameset of ePDCCH resources correspond to quasi co-located antenna portsand, optionally, (2) whether the RS ports or some subset of the RS portsin the two different sets of ePDCCH resources correspond to quasico-located antenna ports. The information provided in step 702 may beprovided by, for example, RRC signaling. Note that while steps 700 and702 are illustrated as separate steps, steps 700 and 702 may beperformed using a single message.

Sometime thereafter, the RAN 12 transmits a downlink subframe thatincludes ePDCCH (step 704). The WD 16 estimates one or more large-scalechannel properties for an RS port within a set of ePDCCH resources basedon RSs, or more specifically reference symbols in RS ports, thatcorrespond to quasi co-located antenna ports as indicated in theinformation received from the RAN 12 in step 702 (step 706). The WD 16then utilizes the one or more large-scale channel estimates as discussedabove (step 708).

FIG. 24 illustrates the operation of the cellular communications network10 according to one embodiment in which the WD 16 receives ePDCCH fromtwo different base stations 14 (i.e., two different transmissionpoints). As illustrated, in this embodiment, one of the base stations 14(base station 14 corresponding to transmit point 1) transmitsconfiguration information to the WD 16 that configures ePDCCH resources,namely, a first set of ePDCCH resources for transmit point 1 and asecond set of ePDCCH resources for transmit point 2 (steps 800 and 802).In addition to configuring the ePDCCH resource sets, the base station 14transmits quasi co-located antenna information to the WD 16 (step 804).In this embodiment, the quasi co-located antenna information indicatesthat the WD 16 can assume that antenna ports, or the corresponding RSports, in the same ePDCCH resource set are quasi co-located. Notably,while steps 800-804 are illustrated as separate steps, the correspondinginformation may be transmitted in a single message.

Sometime thereafter, the base station 14 corresponding to transmit point1 transmits a downlink subframe including ePDCCH transmission(s) in thefirst set of ePDCCH resources to the WD 16 (step 806). In the samedownlink subframe, the base station 14 corresponding to transmit point 2transmits ePDCCH transmission(s) in the second set of ePDCCH resources(step 808). The WD 16 estimates one or more large-scale channelproperties for an RS port within the first set and/or the second set ofePDCCH resources based on RSs, or more specifically reference symbols inRS ports, in the same set of ePDCCH resources (step 810). Thus, the WD16 estimates the one or more large-scale channel properties for an RSport in the first set of ePDCCH resources based on all of the other RSports in the first set of ePDCCH resources, which for this embodimentcan be assumed by the WD 16 to correspond to quasi co-located antennaports. Likewise, the WD 16 estimates the one or more large-scale channelproperties for an RS port in the second set of ePDCCH resources based onall of the other RS ports in the second set of ePDCCH resources, whichfor this embodiment can be assumed by the WD 16 to correspond to quasico-located antenna ports. The WD 16 then utilizes the one or morelarge-scale channel estimates as discussed above (step 812).

FIG. 25 is a block diagram of one of the WDs 16 according to oneembodiment of the present disclosure. As illustrated, the WD 16 includesa radio subsystem 18 and a processing subsystem 20. The radio subsystem18 generally includes analog and, in some embodiments, digitalcomponents for sending and receiving data to and from the base stations14. In particular embodiments, the radio subsystem 18 may represent orinclude one or more Radio Frequency (RF) transceivers, or separate RFtransmitter(s) and receiver(s), capable of transmitting suitableinformation wirelessly to and receiving suitable information from othernetwork components or nodes. From a wireless communications protocolview, the radio subsystem 18 implements at least part of Layer 1 (i.e.,the Physical or “PHY” Layer).

The processing subsystem 20 generally implements any remaining portionof Layer 1 as well as functions for higher layers in the wirelesscommunications protocol (e.g., Layer 2 (data link layer), Layer 3(network layer), etc.). In particular embodiments, the processingsubsystem 20 may comprise, for example, one or several general-purposeor special-purpose microprocessors or other microcontrollers programmedwith suitable software and/or firmware to carry out some or all of thefunctionality of the WD 16 described herein. In addition oralternatively, the processing subsystem 20 may comprise various digitalhardware blocks (e.g., one or more Application Specific IntegratedCircuits (ASICs), one or more off-the-shelf digital and analog hardwarecomponents, or a combination thereof) configured to carry out some orall of the functionality of the WD 16 described herein. Additionally, inparticular embodiments, the above described functionality of the WD 16may be implemented, in whole or in part, by the processing subsystem 20executing software or other instructions stored on a non-transitorycomputer-readable medium, such as Random Access Memory (RAM), Read OnlyMemory (ROM), a magnetic storage device, an optical storage device, orany other suitable type of data storage components. Of course, thedetailed operation for each of the functional protocol layers, and thusthe radio subsystem 18 and the processing subsystem 20, will varydepending on both the particular implementation as well as the standardor standards supported by the WD 16.

FIG. 26 is a block diagram of one of the base stations 14 according toone embodiment of the present disclosure. As illustrated, the basestation 14 includes a radio subsystem 22 and a processing subsystem 24.The radio subsystem 22 generally includes analog and, in someembodiments, digital components for sending and receiving data to andfrom wireless devices, such as the WD 16, within a corresponding cell ofthe cellular communications network 10. In particular embodiments, theradio subsystem 22 may represent or include one or more RFtransceiver(s), or separate RF transmitter(s) and receiver(s), capableof transmitting suitable information wirelessly to and receivingsuitable information from other network components or nodes. From awireless communications protocol view, the radio subsystem 22 implementsat least part of Layer 1 (i.e., the Physical or “PHY” Layer).

The processing subsystem 24 generally implements any remaining portionof Layer 1 not implemented in the radio subsystem 22 as well asfunctions for higher layers in the wireless communications protocol(e.g., Layer 2 (data link layer), Layer 3 (network layer), etc.). Inparticular embodiments, the processing subsystem 24 may comprise, forexample, one or several general-purpose or special-purposemicroprocessors or other microcontrollers programmed with suitablesoftware and/or firmware to carry out some or all of the functionalityof the base station 14 described herein. In addition or alternatively,the processing subsystem 24 may comprise various digital hardware blocks(e.g., one or more ASICs, one or more off-the-shelf digital and analoghardware components, or a combination thereof) configured to carry outsome or all of the functionality of the base station 14 describedherein. Additionally, in particular embodiments, the above describedfunctionality of the base station 14 may be implemented, in whole or inpart, by the processing subsystem 24 executing software or otherinstructions stored on a non-transitory computer-readable medium, suchas RAM, ROM, a magnetic storage device, an optical storage device, orany other suitable type of data storage components.

The following acronyms are used throughout this disclosure.

3GPP 3^(rd) Generation Partnership Project AL Aggregation Level ASICApplication Specific Integrated Circuit BS Base Station CCE ControlChannel Element CoMP Coordinated Multi-Point CRS Common Reference SignalCSI-RS Channel State Information Reference Signal CSS Common SearchSpace DCI Downlink Control Information DFT Discrete Fourier Transform DLDownlink DMRS Demodulation Reference Signal DPS Dynamic Point SelectioneNB Enhanced Node B ePDCCH Enhanced Physical Downlink Control ChannelePHICH Enhanced Physical Hybrid Automatic Repeat Request IndicatorChannel GSM Global System for Mobile Communications HARQ HybridAutomatic Repeat Request JT Joint Transmission kHz Kilohertz LTE LongTerm Evolution ms Millisecond OFDM Orthogonal Frequency DivisionMultiplexing PCFICH Physical Control Format Indicator Channel PDCCHPhysical Downlink Control Channel PDSCH Physical Downlink Shared ChannelPRB Physical Resource Block PSS Primary Synchronization Signal PUSCHPhysical Uplink Shared Channel RAM Random Access Memory RAN Radio AccessNetwork RB Resource Block RE Resource Element REG Resource Element GroupRel-10 Long Term Evolution Release 10 Rel-11 Long Term Evolution Release11 RF Radio Frequency ROM Read Only Memory RRC Radio Resource Control RSReference Signal SSS Secondary Synchronization Signal UE User Element ULUplink UMB Ultra Mobile Broadband WCDMA Wideband Code Division MultipleAccess WD Wireless Device WiMAX Worldwide Interoperability for MicrowaveAccess

Those skilled in the art will recognize improvements and modificationsto the preferred embodiments of the present disclosure. All suchimprovements and modifications are considered within the scope of theconcepts disclosed herein and the claims that follow.

What is claimed is:
 1. A user equipment configured to operate in acellular communications network, comprising: a radio subsystem; and aprocessing subsystem associated with the radio subsystem configured to:receive a downlink subframe comprising a downlink control channel,wherein a search space associated with the downlink control channelcomprises a plurality of sets of downlink control channel physicalresources; and estimate a channel for an antenna port of interest in oneset of the plurality of sets based on an assumption by the userequipment that one or more other antenna ports in the same set of theplurality of sets are quasi co-located with respect to the antenna portof interest.
 2. The user equipment of claim 1 wherein the processingsubsystem is further configured to assume that the antenna port ofinterest is quasi co-located with the one or more other antenna ports inthe same set in accordance with one or more predefined rules that definewhich of the antenna ports are quasi co-located for the downlink controlchannel.
 3. The user equipment of claim 2 wherein antenna ports in adifferent set of the plurality of sets are not assumed to be quasico-located with respect to the antenna port of interest in accordancewith the one or more predefined rules.
 4. The user equipment of claim 1wherein one or more physical resource blocks over which the one or moreother antenna ports are quasi co-located with the antenna port ofinterest are predefined by the cellular communications network.
 5. Theuser equipment of claim 1 wherein the one or more other antenna ports inthe same set as the antenna port of interest are comprised in a firstgroup of antenna ports, and wherein the processing subsystem is furtherconfigured to assume that the antenna port of interest is quasico-located with one or more antenna ports comprised in a second group ofantenna ports in the set in accordance with signaling received from thecellular communications network.
 6. The user equipment of claim 1wherein antenna ports in the same set are quasi co-located with respectto one or more of a group of large-scale channel properties consistingof: delay spread, Doppler spread, Doppler shift, average gain, andaverage delay.
 7. The user equipment of claim 1 wherein the cellularcommunications network is a Long Term Evolution, cellular communicationsnetwork, the downlink control channel is an enhanced Physical DownlinkControl Channel, the one or more sets of downlink control channelphysical resources are one or more sets of enhanced Physical DownlinkControl Channel physical resource block pairs, where each set ofenhanced Physical Downlink Control Channel physical resource block pairsincludes one or more physical resource block pairs in one or moreenhanced Physical Downlink Control Channel regions within the downlinksubframe.
 8. The user equipment of claim 1 wherein the antenna port ofinterest is a Demodulation Reference Signal (DMRS) port.
 9. The userequipment of claim 8, wherein the one or more other antenna ports in thesame set comprise at least one of a group consisting of: at least oneother DMRS port in the same set and at least one Reference Signal (RS)port of a type other than DMRS.
 10. The user equipment of claim 1,wherein each of the plurality of sets of downlink control channelphysical resources is associated with a different transmission point inthe cellular communications network than another one of the plurality ofsets of downlink control channel physical resources.
 11. A method ofoperation of a user equipment in a cellular communications network,comprising: receiving a downlink subframe from the cellularcommunications network, the downlink subframe comprising a downlinkcontrol channel from the cellular communications network, wherein asearch space associated with the downlink control channel comprises aplurality of sets of downlink control channel physical resources; andestimating a channel for an antenna port of interest in one set of theplurality of sets based on an assumption by the user equipment that oneor more other antenna ports in the same set of the plurality of sets arequasi co-located with respect to the antenna port of interest.
 12. Themethod of claim 11 wherein estimating the channel includes: assumingthat the antenna port of interest is quasi co-located with the one ormore other antenna ports in the same set in accordance with one or morepredefined rules that define which of the antenna ports are be quasico-located for the downlink control channel.
 13. The method of claim 12wherein antenna ports in a different set of the plurality of sets arenot assumed to be quasi co-located with respect to the antenna port ofinterest in accordance with the one or more predefined rules.
 14. Themethod of claim 11 wherein one or more physical resource blocks overwhich the one or more other antenna ports are quasi co-located with theantenna port of interest are predefined by the cellular communicationsnetwork.
 15. The method of claim 11 wherein the one or more otherantenna ports in the same set as the antenna port of interest arecomprised in a first group of antenna ports, wherein estimating thechannel includes: assuming that the antenna port of interest is quasico-located with one or more antenna ports comprised in a second group ofantenna ports in the set in accordance with signaling received from thecellular communications network.
 16. The method of claim 11 whereinantenna ports in the same set are quasi co-located with respect to oneor more of a group of large-scale channel properties consisting of:delay spread, Doppler spread, Doppler shift, average gain, and averagedelay.
 17. The method of claim 11 wherein the cellular communicationsnetwork is a Long Term Evolution, cellular communications network, thedownlink control channel is an enhanced Physical Downlink ControlChannel, the one or more sets of downlink control channel physicalresources are one or more sets of enhanced Physical Downlink ControlChannel physical resource block pairs, where each set of enhancedPhysical Downlink Control Channel physical resource block pairs includesone or more physical resource block pairs in one or more enhancedPhysical Downlink Control Channel regions within the downlink subframe.18. The method of claim 11 wherein the antenna port of interest is aDemodulation Reference Signal (DMRS) port.
 19. The method of claim 18,wherein the one or more other antenna ports in the same set comprise atleast one of a group consisting of: at least one other DMRS port in thesame set and at least one Reference Signal (RS) port of a type otherthan DMRS.
 20. The method of claim 11, wherein each of the plurality ofsets of downlink control channel physical resources is associated with adifferent transmission point in the cellular communications network thananother one of the plurality of sets of downlink control channelphysical resources.